Jacqui Press has dissected the singer's fiery confrontation from Tuesday's "Marcello Mio" premiere -- and she says it all kicked off smoothly, with KR graciously telling the security guard, "It's OK," after she accidentally stepped on her dress. But then things took a drastic turn!

Jacqui spills to MailOnline that the security guard's response is still a bit fuzzy, but it was enough to irk Kelly 'cause she apparently fired back with a firm, "Don't talk to me like that."

From the clip, you can see the security guard trying to keep her cool as she continues ushering Kelly up the stairs. But Kelly keeps turning back, wagging her finger, and repeating, "Don't talk to me like that!"

Adding more drama to the scene, a male security guard also intervenes, asking what all the commotion's about. But Kelly ain't backing down ... asserting one final time, "You still don't talk to me like that!"

Internet sleuths online also came to the general consensus Kelly was telling the woman not to speak to her in the way she had -- but obviously, we still don't know what exactly was said to get her seeing red.

This is the second heated exchange Kelly's been involved in this year -- Remember, she sparked controversy in Feb after walking off the 'Today' show set over dressing room issues.